The present invention relates to a method for manufacturing a honeycomb structure and to a honeycomb structure. More specifically, the present invention relates to a method for manufacturing a honeycomb structure capable of obtaining a well-formed honeycomb structure even when the water content in kneaded clay is small and to a honeycomb structure obtained by the manufacturing method.
A ceramic honeycomb structure is used in order to trap dust and particulate matter contained in exhaust gas from an automobile, incineration exhaust gas generating upon incineration of waste and the like and, further, in order to adsorb and absorb NOx, CO, HC and the like in the aforementioned exhaust gases with a loaded catalyst. Among such honeycomb structures, a cordierite based honeycomb structure is used as one excellent in thermal shock resistance (see JP-A-11-92214 and JP-A-11-100259).
As a method for manufacturing such a cordierite based honeycomb structure, there is disclosed, for example, a method of manufacturing a ceramic structure, where a ceramic raw material (forming mixture), water, an organic binder, and the like are kneaded to obtain kneaded clay having improved plasticity (flowability), and the kneaded clay is subjected to extrusion forming, followed by drying and firing (see Japanese Patent No. 3227039). The reason why the kneaded clay contains an organic binder is because plasticity (flowability), shape retainability, and the like required for the forming cannot be obtained sufficiently only by the ceramic raw material powder and water. The addition of an organic binder and the like improves extrusion formability (balance between flowability and shape retainability). Besides, as a manufacturing method for improving extrusion formability, for example, there is a method where a fatty acid salt having a specific carbon number is blended as a dispersant at a certain proportion. This enables to manufacture a honeycomb structure having excellent extrusion formability with high productivity and is a honeycomb structure-manufacturing method capable of reducing a load to a forming apparatus (Japanese Patent No. 3799241).
Besides, as a manufacturing method for improving extrusion formability, for example, there is disclosed a method for manufacturing a honeycomb structure, where the forming mixture contains two or more kinds of magnesium-containing substances including at least talc (first magnesium-containing substance), and the magnesium-containing substances (second magnesium-containing substance) other than talc among the magnesium-containing substances has an average particle diameter of 4 μm or less (WO2006/046542). This enables to obtain a well-formed honeycomb structure even when the content of the organic substance in kneaded clay is low.
When an organic binder is added in order to improve extrusion formability, the proportion of water to be blended becomes high to require a vast amount of energy upon drying the formed article and a long drying time, which causes a problem of easy deformation. In addition, when an organic forming auxiliary (e.g., fatty acid salt) is further added to the organic binder, the amount of CO2 generating upon firing is increased to cause a problem of generating an environmental load. Further, when magnesium-containing substances other than talc is used at 40 mass % or more with respect to the total amount of the magnesium-containing substances as the magnesium-containing substances, the thermal expansion coefficient rises to cause a problem of deterioration in thermal shock resistance.